With progression of mobile instruments in recent years, development of electrochemical devices such as batteries and capacitors using electrochemical phenomena has been actively carried out to obtain power sources for the instruments. Additionally, as electrochemical devices other than power sources, an electrochromic display (ECD) making change in color under electrochemical reaction is given.
Each of these electrochemical devices is generally constituted of a pair of electrodes and an ion conductive body filling a space between the electrodes. As this ion conductive body, one prepared by dissolving salts (AB) including cation (A+) and anion (B−), called electrolyte, in a solvent, a polymer or a mixture thereof is used. By dissolving this electrolyte, it dissociates into cation and anion thereby making an ion conduction. In order to obtain an ion conductivity required for the devices, it is necessary that a sufficient amount of the electrolyte is dissolved in the solvent or the polymer. In practice, there are many cases of using as the solvent ones other than water, in which electrolytes having sufficient solubilities to such organic solvents or polymers can be presently limited to several kinds. For example, only LiClO4, LiPF6, LiBF4, LiAsF6, LiN(CF3SO3)2 and LiCF3SO3 are used for the electrolyte of a lithium ion battery. The section of cation is almost decided by a device like lithium ion of a lithium battery, whereas the section of anion is usable if the condition of having a high solubility is satisfied.
The most appropriate electrolytes for the respective applications have been searched under a circumstance where a wide variety of application ranges are required for the devices; however, searching the most appropriate ones have reached a limit because kinds of anion are presently little. Additionally, present electrolytes have a variety of problems, and therefore electrolytes having a new anion section has been required. Specifically, ClO4 ion is explosive and AsF6 ion has a toxicity, and therefore they cannot be used from the viewpoint of safety. LiN(CF3S2) and LiCF3SO3 are difficult to be used because they corrode a collector of aluminum in a condition where an electric potential is applied. Only LiPF6 put into practical use also has the problems in heat resistance and in hydrolysis resistance.
Some compounds have been hitherto proposed as electrolytes having a new anion section. For example, lithium bis(biphenyldiolato) borate has been proposed as a new electrolyte (see Patent Citation 1); however, it is problematic because of being insufficient in solubility to nonaqueous organic solvent and oxidation resistance in the battery. Additionally, lithium bis(salicylato) borate and one in which an electron attractive CI is bonded as a substituent to a ligand of lithium bis(salicylato) borate have been proposed as new electrolytes; however, lithium bis(salicylato) borate is insufficient in ion conductivity and oxidation resistance, and the CI-substituted derivative is problematic to be excessively low in solubility though it is improved in ion conductivity and oxidation resistance.
Additionally, concerning battery as an electrochemical device, attention has been paid in recent years on small-size electricity storage systems for high energy density applications such as intelligence instrument and communication equipment such as personal computer, video camera, digital still camera, mobile phone and the like, and on large-size electricity storage systems for power applications such as electric vehicle, hybrid vehicle, auxiliary power source for fuel cell vehicle, power storage and the like. One proposed for them is lithium ion battery, lithium battery, lithium ion capacitor or the like which has been actively developed.
Many of these nonaqueous electrolyte batteries have been put into practical use; however, these cannot be satisfied in a variety of applications from the viewpoint of durability, in which they are highly deteriorated particularly at a temperature of not lower than 45° C. and therefore problematic for applications of being used for a long period of time and in a site high in temperature, for example, automotive vehicle.
In general, in these nonaqueous electrolyte batteries, a nonaqueous electrolytic solution or a nonaqueous electrolytic solution which is formed into a quasi-solid state with a gelating agent is used as an ion conductive body. The configuration of it is as follows: One kind or a mixture solvent of several kinds selected from aprotic ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and the like are used as a solvent, and lithium salt such as LiPF6, LiBF4, (CF3SO2)2NLi, (C2F5SO2)2NLi or the like is used as a solute.
As measures for improving the cycle characteristics, high temperature storage stability and durability of a nonaqueous electrolyte battery, optimization of various constituting elements of the battery including active material of a positive electrode and a negative electrode has been hitherto studied. Techniques relating to nonaqueous electrolytic solution are also no exception, in which it has been proposed to suppress deterioration of the electrolytic solution at the surfaces of the active positive and negative electrodes due to decomposition of the electrolytic solution by using a variety of additives. It has been proposed to suppress the deterioration and improve battery characteristics, for example, by adding vinylene carbonate (see Patent Citation 2) to an electrolytic solution or by adding cyclohexyl benzene or tetrahydronaphthalene (see Patent Citation 3) to an electrolytic solution. However, it is insufficient in effect to suppress the deterioration at a high temperature of not lower than 45° C., accompanying a problem that a resistance within the battery rises. Accordingly, a further improvement in characteristics of the electrolytic solution has been desired.